De novo mutations in the gene encoding methyl CpG binding protein 2 (MeCP2) are the primary cause of Rett Syndrome (RTT), an X-linked dominant neurodevelopmental disorder. Mecp2 is a chromatin-associated protein that has long been considered to be a non-specific transcriptional repressor of methylated DNA. However, recent data indicate that Mecp2 can interact with specific transcriptional regulators to alter contextual gene expression. Consistent with the pronounced neurological phenotype in RTT patients, emerging evidence suggests a close association between Mecp2 activity and neuronal function. In the mammalian nervous system, Mecp2 expression is highest in postmitotic neurons, where a newly identified splice variant, Mecp2e1, is the predominant transcript. Similarities in phenotype and neuropathology caused by mutations in Mecp2 suggest that the neuronal function of Mecp2 is conserved between humans and mice. The goals of this proposal are to better understand the regulation and activity of Mecp2 in the nucleus of cultured neuronal cells and determine how mutation and serine phosphorylation affect its function. The work proposed will use live cell imaging approaches to examine the mobility of Mecp2 in the nucleus and explore the consequences of mutation, chromatin remodeling and phosphorylation on chromatin binding. We will specifically characterize a newly identified splice variant of the protein that is the relevant isoform in the disease. We will also characterize the role of nerve growth factor and target innervation in regulation of Mecp2 expression and function in sympathetic neurons and determine how Mecp2 deficiency affects the ability of a sympathetic neuron to respond to physiologic cues. Together these studies should answer fundamental questions about the ways that sympathetic neurons modulate Mecp2 function, through isoform specific expression and post-translational modification. These studies will help clarify the way that the Mecp2 protein is regulated and test the ways in which disease causing mutations affect the protein's function. The long term goals are to understand the pathogenesis of the dysfunction of the nervous system in patients with RTT and determine ways that the system can be modulated to potentially improve function and develop targeted therapies.